Study of LFD-200 in Healthy Adults and Adults With Moderate to Severe Rheumatoid Arthritis

This is a double-blind, randomized, placebo- and active-controlled study investigating the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of subcutaneous (SC) doses of LFD-200. The study design includes: a single ascending dose (SAD) study in up to 66 adult healthy participants (HPs) to investigate the effects of a single SC dose, with a 30-day follow-up; a multiple ascending dose (MAD) study in up to 40 HPs to assess up to 4 weekly SC doses, with a 30-day follow-up after the last dose; and a MAD study in up to 70 participants with moderate to severe rheumatoid arthritis (RA) to evaluate up to 13 weekly SC doses, with a 30-day follow-up after the last dose.

Inclusion Criteria for Healthy Participants: * Age 18-55 * BMI - 18-32 * Participants must be deemed by the Investigator to be generally healthy individuals based on a medical evaluation that includes a physical examination, medical history, vital signs, and the results from clinical labs and other safety assessments collected during the Screening period. Exclusion Criteria for Healthy Participants: * Participants with any current or previous illness that, in the opinion of the investigator, might confound the results of the study or pose an additional, unacceptable risk to the participant or that could prevent, limit, or confound the protocol specified assessments or study results' interpretation. * Recent serious or ongoing infection * Known/suspected primary immunodeficiency * Receipt of injected or systemic glucocorticoids within 6 weeks prior to screening * Use of prohibited medications * Any of the following lab abnormalities: * White blood cell (WBC) count \